The present invention relates to sulfanylsilanes, a process for the preparation thereof and their use.
It is known that sulfur-containing organosilicon compounds such as 3-mercaptopropyltrimethoxysilane or bis-(3-[triethoxysilyl]-propyl)tetrasulfane are used as silane coupling agents or reinforcing additives in oxidically filled rubber mixtures, inter alia for tire treads and other parts of car tires (DE 21 41 159, DE 22 12 239, U.S. Pat. No. 3,978,103, U.S. Pat. No. 4,048,206).
Furthermore, it is known that sulfur-containing silane coupling agents are used during the preparation of sealing compounds, casting moulds for metal goods, coloured and protective paints, adhesives, asphalt mixtures and oxidically filled plastics.
Other possible applications are for the fixing of active substances and functional units to inorganic support materials, for example for the immobilization of homogeneous catalysts and enzymes, for the production of fixed bed catalysts and for liquid chromatography.
The use of mercaptosilanes in rubber mixtures for tire treads is disclosed in the patent FR-A-2.094.859. Known mercaptosilanes and in particular 3-mercaptopropyltrimethoxysilane and 3-mercaptopropyltriethoxysilane are able to produce improved properties with regard to silica/elastomer coupling. The industrial use of these is not possible due to the high reactivity of the SH groups, because, during the production of the mixture, they lead to very rapid pre-vulcanization, also known as pre-scorch, with greatly increased Mooney plasticity and ultimately to mixtures which are almost impossible to process and use in an industrial situation.
For other applications such as, for example, industrial rubber items which are processed in a different way, mercaptosilanes may be used as reinforcing additives. However, in the case of almost all organic mercaptans, their intrinsic, extremely unpleasant and penetrating odor has proven to be a problem which can be only slightly reduced by mechanical means.
As a result of the pre-scorch phenomenon mentioned above, polysulfidic organosilanes, including bis-3triethoxysilyl-propyltetrasulfane or bis-3-triethoxysilylpropyldisulfane (DE 25 42 534, DE 24 05 758, DE 195 41 404, DE 197 34 295) are mostly used as coupling agents for tire treads, these seeming to be the best compromise for silica-filled vulcanizates with regard to reliability of vulcanization, simplicity of production and reinforcing power. However, these coupling reagents have to be used in relatively large amounts. Approximately 2 to 3 times as much as the amount of 3-mercaptopropyltrimethoxysilane are required to produce an equivalent level of coupling properties.
This disadvantage led to a few attempts to get round the processing difficulties by using better, in the sense of reinforcing properties, mercaptosilanes. An attempt of this kind is described in the U.S. Pat. No. 4,474,908. But this method did not produce satisfactory results with regard to scorching and processing problems and in addition is costly. Furthermore, patent EP 0 784 072 A1 describes the use of functional polyorganosiloxanes in addition to a mercaptosilane, which enabled, for the first time, the processing of mercaptosilanes as reinforcing agents in rubber mixtures for tire treads.